The present invention relates to a machineing system including a plurality of machining tools, and a control system useful for controlling the operation of the machining system.
Direct numerical control systems (which will be hereinafter referred to as DNC systems) have been known as typical systems for supplying various types of workpieces to a plurality of universal type machine tools such as machining centers. In such a system, a central computer processes all the information necessary for each machine tool, such as information about machining, information about tool exchange, and information about transfer of pallets carrying a workpiece into and out of the working area, and directly provides the movable members of the machine tool with numerical values representing the amount of the desired movement in the X, Y and Z axis directions. However, the DNC system generally is not economical unless there are about ten or more machine tools. Moreover, in a DNC system, the central computer is closely coupled with machine tools and workpiece conveyors, so that failure occurring in a part of the system, particularly in the central computer will disable operation of the entire system. Thus, adoption and operation of the DNC system require highly developed production control organization and computer software. For these reasons, various operation control systems for a plurality of machine tools which differ from the DNC systems have been proposed. One of them is a type wherein a numerical control device (which will be hereinafter referred to as an NC device) is provided for each of the machine tools, and separate operation of each machine tool is enabled.
In the afore-mentioned operation control system, various systems have been used, in place of the DNC system, for control over the conveyance of the pallets and transfer of pallets into and out of the working area of each machine tool. In a system which is frequently used, pallets are arranged for each machine tool in a predetermined order, and these pallets are sequentially supplied to the machine tool. In these systems, it is necessary to obtain data on various conditions such as: which pallet is in the pallet change position for each machine tool; whether or not the part program for the workpiece on the pallet is stored in the NC system; and whether or not instruction should be given to the pallet change device to introduce the pallet into the working area of the machine tool, and sequence operation for introducing the pallet must be carried out before execution of the part program. Control programs or instructions for various operations such as sequence operations on the conveyance of the pallets, and introduction of the pallet into the working area of each machine tool following an instruction for selecting the particular pallet are stored in a memory of a controller separately provided. But, even under these circumstances, programs supplementing the control program stored in the controller for driving the pallets are included in the system program in each NC device. According to a recent trend, a part program is made to contain instructions for selecting a pallet and for transferring the pallet. Provided at the pallet stop positions on the pallet conveyance line are sensing devices for locating the pallets.
The above-described is a problem of how to construct and how to drive the pallet magazine, and in a different viewpoint, a problem of how to control the pallet magazine in accordance with part of a part program or part of a system program in an NC device supplementing the control program. The part of the program concerning drive and contrl of the pallets in relation to transfer of pallets to and from the machine tool is referred to as a PA program.
Described hereinabove are mainly problems concerning conveyance line of the pallets and introduction and withdrawal of pallets.
In addition, there are problems associated with preparation of part programs. Tool numbers for identifying tools used for machining are designated in each part program and whether or not processes of "adaptive control" such as regulated feed rate control for targeted load should be performed for the particular tools is also specified in each part program. Whether or not program steps of tool breakage detection are adopted is also specified in each part program. Moreover, data concerning the diameter and the length of the tools necessary for path compensation and a code for calling such data from a different memory are specified in each part program. Incorporating these data and instructions concerning tools into a part program which already contains instructions concerning the specific pallets will add complication to preparation of the part program.
Preparation of a part program must, of course, be completed before the actual machining of the workpiece takes place.
It should also be noted that roles are usually divided between a programming department for preparing part programs and a machining department for manufacturing the product where machining on the workpieces actually takes place. It is with various difficulties for the programming department to prepare programs upon thorough understanding of various technical information and production control information which are known in the manufacture department. Decisions on the details such as whether or not the processes of tool breakage detection or adaptive control are to be adopted and how many spare tools should be stored in the tool magazine are difficult for the programmer to make and are better made by the operators in the manufacture department.
Moreover, in which order the workpieces on the respective pallets which may be as many as several tens in number should be machined by one or two machining centers and in what procedures the workpieces should be mounted on a pallet are matters of the nature to be decided by the manufacture department at its own convenience.
Having the programming department prepare a part program will lead to reduction of versatility or flexibility of the resultant program. For instance, if a machining center does not have a function of adaptive control such as regulated feed rate control for targeted load, a part program containing adaptive control instructions cannot be loaded in the NC device for use with the above-mentioned machining center. Also, a part program containing a process of detection of tool breakage cannot be loaded in an NC device which does not have a supervisory program for the tool breakage detection. Two examples have been raised in connection with the reduction of versatility of a part program. It will be understood from these examples that the versatility of a part program is progressively reduced (and hence a part program has to be re-prepared) as the various functions (tool breakage detection, adaptive control, tool radius compensation, tool length compensation, and the like) are added.